One of the most important and technically challenging applications of fluidic sensors is in the assessment and protection of the quality of a gas, gas mixture, or liquid media ambient to a defined environment, whether such gas or other fluid is flowing or static within said environment. An example of such an application is the monitoring and protection of air typically delivered to an enclosed public place by a heating, ventilation, air conditioning (HVAC) system. Such an enclosed public place could be vulnerable to intentional or unintentional contamination by potentially harmful chemical gases or airborne biological agents introduced into the HVAC system.
The prior art contains attempts to mimic the mammalian olfaction system in the design of fluidic sensor systems. The resemblance between signal processing from multiple olfactory centers and pattern recognition technique for processing the responses of a fluidic sensor array has led to the descriptor “electronic nose,” which has been successful in some applications.
The concept of an “electronic nose” generally involves the use of chemical sensors that can detect certain gas chemicals present within environmental air. Such chemical sensors operate using a chemical or biochemical reaction, in which specific reactants and catalysts must meet. In such sensors, a mass transfer step must occur to deliver reactant(s) to the surface(s) of the sensor(s) to reach catalyst(s) therein before a reaction can occur. The rate of a reaction is thus limited by the time required for diffusion of reactant(s) to the sensor surface(s).
Prior art efforts at use of an “electronic nose” in exemplary applications to monitor ambient air for potentially harmful chemical or biological contaminants has been limited by the speed at which existing sensors systems can complete the requisite reactions and provide a warning of the presence of a chemical or biological hazard. Some sensors are limited in such applications by diffusion-limited mass transfer at the surface of the sensing elements within the sensors.